This invention relates to a rotary drum comprising a bearing ring loosely mounted on the drum shell and spacer plates loosely arranged between the drum shell and the bearing ring and which are secured in the axial and peripheral direction of the drum shell by means of retaining elements, but which are displaceable to a limited extent relative to the bearing ring and/or the drum shell, at least in the axial direction.
In rotary drums of the type used for the heat-treatment of bulk materials, for example revolving tubular kilns, drying drums, cooling drums and the like, at least one bearing ring is mounted on the drum shell by means of which the drum shell rests on supporting rollers, at least one bearing ring being loosely arranged on the drum shell so that it does not rotate with the shell. This loose bearing ring has minimal clearance from the outer periphery of the drum shell and has to be guided in the axial direction of the rotary drum. In heat-treatment drums of the type in question, particular importance is attached to the clearance to be maintained between the loose bearing ring and the outer periphery of the drum shell, particularly when considerable fluctuations in temperature occur, as is the case above all with revolving tubular kilns. This is because, if the clearance referred to is too great, the bearing strength of the bearing ring is not fully utilized and serious deformations, particularly in the form of ovalities, can occur in operation with the result that, for example, a lining, refractory cladding or the like provided on the inside of the drum shell is destroyed in the region of this loose bearing ring. If, on the other hand, the clearance referred to is too small, necking of the drum shell can occur in the region of this bearing ring during the heating of a revolving tubular kiln for example and can also result in undesirable deformation of the shell and hence in damage to internal linings of the drum shell.
Various constructions for retaining a loose bearing ring on the drum shell are known in practice. In most cases, spacer plates are used, being inserted between the loose bearing ring and the drum shell. In the event of an excessive change in the clearance from the bearing ring, these spacer plates may be replaced by other spacer plates.
In one known construction, the spacer plates are screwed or welded onto the outside of the drum shell. However, this method of fixing the spacer plates on the drum shell is attended by two serious disadvantages. Since a drum shell is exposed to considerable deformation in operation, a sudden increase in rigidity relative to the drum shell occurs in the region of the spacer plates thus secured which can lead to damage to the spacer plates, to the fixing points and to the drum shell. If, in addition, the spacer plates have to be replaced due to a change in the clearance between the bearing ring and the drum shell, the necessary replacement can only be effected by removing old spacer plates and fitting new ones, both of which involve complicated operations.
In another known construction, an attempt is made to overcome the disadvantages referred to above by loosely arranging the spacer plates between the drum shell and the loose bearing ring and subsequently fixing them with minimal axial clearance from the drum shell and the bearing ring by means of angular retaining elements which are welded onto the drum shell. For securing the loose bearing ring in the axial direction of the drum shell, additional retaining elements or the like are welded onto the drum shell. With this known construction, however, two points have to be borne in mind. Firstly, the spacer plates are rolled down to a certain extent by the bearing ring in operation so that they become longer, this increase in length having to be taken into consideration when establishing the axial clearance by means of the angular retaining elements. Secondly, however, it is important to obtain minimal clearance in the axial direction which is important above all to the axial guidance of the bearing ring. This second point is of importance above all in the case of rotary drums used for heat-treatment, particularly in the case of a revolving tubular kiln because, in the event of sudden cooling of the drum shell, strong axial forces and stresses occur. In addition, it is necessary in this known construction, too, to remove at least some of the angular retaining elements holding the spacer plates from the furnace mantle for the purpose of replacing spacers; the same applies when the bearing ring has to be replaced. To remove welded-on retaining elements and to refit new ones in this way is not only time consuming and labour-intensive, but also results in undesirable weakening of the drum shell in these fixing zones.